1. Field of the Invention
The present invention relates to face milling cutters and cutter bodies thereof, and more specifically to a face milling cutter having a groove for a cartridge preventing the cartridge type holder for an insert from flying out under centrifugal force and a cutter body thereof.
2. Description of the Background Art
In most cases, a wedge is used for clamping an insert in a face milling cutter. In this case, the insert is inserted into a groove which is formed both in front and side surfaces of a cutter body, so that it is held in place only by friction force. In the conventional method, however, if strong centrifugal force acts on the insert due to the high speed rotation of the cutter body, the insert is often shifted during cutting operation. In an extreme case, the insert may even fly out of the groove.
FIG. 7 is a diagram shown in conjunction with a typical method of fixing the insert in the conventional face milling cutter. In the conventional face milling cutter shown in FIG. 7, a wedge is used to prevent flying out of the insert under centrifugal force.
Referring to FIG. 7, a groove 101 and a wedge groove 103 are formed in a cutter body 100. An insert 104 is arranged in edge groove 101. A wedge 102 is pressed and fitted in wedge groove 103.
It is difficult to form with accuracy an acute angle corner 700 of edge groove 101 and an acute angle corner 600 of wedge groove 103 in which wedge 102 is press fitted as vertical angles thereof are acute. Thus, insert 104 and edge groove 101 as well as wedge 102 and wedge groove 103 are not provided with sufficient accuracy in shape, whereby positional accuracy of the edge and stability of clamping are decreased. As a result, insert 104 may be slightly shifted under centrifugal force developed during high speed rotation of cutter body 100. Further, wedge 102 may become loose due to vibration during cutting, so that insert 104 is slightly shifted. Thus, the conventional face milling cutter lacks in reliability.
To solve this problem, a mechanism having a groove in a cutter body to receive an insert which is clamped by a wedge is proposed in Japanese Patent Laying-Open No. 5-138423. FIGS. 8 and 9 are diagrams shown in conjunction with a conventionally proposed method of fixing the insert in the face milling cutter. Here, the grooves are formed in cylinder and polyhedron shapes in FIGS. 8 and 9, respectively.
Referring to FIG. 8, a groove 151 is formed generally in parallel to an axial center of cutter body 100 by cutting cutter body 100. An insert body 152 has a face 153. An edge (not shown) is connected to insert body 152 with a prescribed angle to face 153. A wedge 154 is fixed to cutter body 100 by a double screw 155 while abutting against face 153 of insert body 152.
In this configuration, even if wedge 154 becomes more or less loose, insert body 152 would not fly out under centrifugal force because of an overhanging portion 100a. In addition, edge groove 151 can be easily formed simply by cutting to open a through hole in a direction of a side surface of cutter body 100.
Referring to FIG. 9, in another conventional example, a groove 161 in a rectangular shape is formed by cutting cutter body 100 generally in parallel to the axial center of cutter body 100. An insert body 162 has an inclined face 163. An edge (not shown) is connected to insert body 162 with a prescribed angle to an abutting face 164. A wedge 154 is fixed to a cutter body 100 by a double screw 155 while abutting against inclined face 163 of insert body 162.
Again, even if wedge 154 becomes loose, insert body 162 would not fly out under centrifugal force because of an overhanging portion 100a of cutter body 100.
In short, in the aforementioned laid open application, grooves 151 and 161 are respectively formed in cylinder and polyhedron shapes to receive insert bodies 152 and 162, with reference to FIGS. 8 and 9. Insert bodies 152 and 162 are clamped with wedge 154 which is movable in a direction orthogonal to edge grooves 151 and 161. Accordingly, movement of insert bodies 152 and 162 in a radial direction of cutter body 100 is restrained by overhanging portion 100a. As a result, the stability of clamping is not decreased even in the case of the high speed rotation and shifting or flying out of insert bodies 152 and 162 under centrifugal force is surely prevented, whereby stability and accuracy for cutting process is effectively increased.
Referring to FIG. 8, however, face 153 of insert body 152 and wedge face 154a of wedge 154 are fixed by friction between the inner surface of edge groove 151 and the outer surface of insert body 152. Thus, application of cutting force makes insert body 152 slightly shift in edge groove 151. Then, the cutting angle of the edge with respect to face 153 slightly differs from those of the other edges. As a result, the edge having the different cutting angle is subjected to a stress which is also different from that of the other edges in magnitude. Accordingly, the edge having the different cutting angle suffers from a problem that positional accuracy and stability thereof are disadvantageously reduced.
Further, referring to FIG. 9, formation of edge groove 161 in such a polyhedron shape in cutter body 100 requires a slotter, wire cutter or electric discharge machine. Any of these machines has a problem in that it disadvantageously increases the number of manufacturing steps and manufacturing cost, or it is not provided with sufficient machining accuracy. Especially, cutter body 100 with a diameter exceeding 300mm requires a large wire cutter machine and hence considerably increases the manufacturing cost.